The purpose of the proposed research is to enumerate both T and B lymphocytes and macrophages in the spleens of mice infected with P. yoelii, P. chabaudi, P. vinckei, and P. berghei. Characterization of the cellular defects responsible for the suppression of the in vitro antibody response to the T-independent antigen, Dextran, will be undertaken using all four species of plasmodia. Finally, Ly subsets of T lymphocytes responsible for the loss of splenic macrophage accessory cell function in antibody formation will be identified.